FIG. 1 is a structural diagram illustrating a Long Term Evolution (LTE) mobile communication system. The LTE system is an evolved version of a conventional Universal Mobile Telecommunications System (UMTS), and is being standardized under the 3rd Generation Partnership Project (3GPP) collaboration agreement.
An LTE network may be generally classified into an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) and a Core Network (CN). The E-UTRAN includes at least one eNode-B serving as a base station. The E-UTRAN also includes an Access Gateway (AG) located at the end of the network so that it is connected to an external network.
The AG may be classified into a user-traffic processing unit and a control-traffic processing unit. In this case, a first AG for processing new user traffic data may communicate with a second AG for processing control traffic data via a new interface. A single eNode-B may include at least one cell. A first interface for transmitting user traffic data or a second interface for transmitting control traffic data may be located between several eNode-Bs. The CN includes the AG and a plurality of nodes for registering users of User Equipments (UEs). If required, another interface for discriminating between the E-UTRAN and the CN may also be used in the LTE network.
Two important elements of the LTE network are an eNode-B and a UE. Radio resources of a single cell include uplink radio resources and downlink radio resources. The eNode-B allocates and controls the uplink and downlink radio resources. In more detail, the eNode-B determines which one of a plurality of UEs will use specific radio resources at a specific time. After performing determination, the eNode-B informs the specific UE of its decision, such that the eNode-B controls the UE to receive the downlink data. For example, the eNode-B may allocate radio resources ranging from 100 MHz to 101 MHz to a specific UE (e.g., No. 1 UE) after the lapse of a predetermined time of 3.2 seconds. Accordingly, the eNode-B may transmit downlink data to the No. 1 UE during a specific time of 0.2 seconds after the lapse of the predetermined time of 3.2 seconds.
In this way, the eNode-B determines which one of the plurality of UEs will perform uplink data transmission and the amount of radio resources the UE can use at a specific time. Moreover, the eNode-B determines a duration of time the UE has to transmit the uplink data.
Compared with a conventional art Node-B or base station, the above-mentioned eNode-B can effectively and dynamically manage radio resources. In the conventional art, a single UE is controlled to continuously use a single radio resource during a call connection time. However, considering the existence of a variety of recent services based on Internet Protocol (IP) packets, the conventional art is ineffective. For example, most packet services have several intervals, wherein no data is transmitted and no packets are generated during the call connection time. Thus, if radio resources are continuously allocated to only one UE, as in the conventional art, the allocation scheme is deemed ineffective. In order to solve this and other problems, the E-UTRAN system has been designed to allocate radio resources to a UE only when there is a need to use the UE, such as when service data is to be transmitted to the UE.
Uplink and downlink channels for transmitting data between the network and the UE will hereinafter be described in detail. There exist downlink channels for transmitting data from the network to the UE, such as a Broadcast Channel (BCH) for transmitting system information, and a downlink Shared Channel (SCH) and downlink Shared Control Channel (SCCH) for transmitting user traffic data or control messages. The traffic data or control messages of a downlink multicast service or broadcast service may be transmitted over the downlink shared channel (SCH), or additionally over a Multicast Channel (MCH). Furthermore, there also exist uplink channels for transmitting data from the UE to the network, such as a Random Access Channel (RACH), and an uplink shared channel (SCH) and uplink shared control channel (SCCH) for transmitting user traffic data or control messages.
FIG. 2 and FIG. 3 are conceptual diagrams illustrating a radio interface protocol structure between the UE and the UMTS Terrestrial Radio Access Network (UTRAN) based on a 3GPP radio access network standard.
The radio interface protocol horizontally includes a physical layer, a data link layer and a network layer. The radio interface protocol vertically includes a User Plane for transmitting data or information and a Control Plane for transmitting a control signal (also called “signaling data”). The protocol layers shown may be classified into a first layer (L1), a second layer (L2) and a third layer (L3) based on three lower layers of a well-known interconnection scheme, such as an Open System Interconnection (OSI) reference model.
The physical layer acting as the first layer (L1) provides an Information Transfer Service over a physical channel. A radio resource control (RRC) layer located at the third layer (L3) controls radio resources between the UE and the network. For this purpose, the RRC layer exchanges RRC messages between the UE and the network. The RRC layer may be distributed to a plurality of network nodes (i.e., eNode-B and AG, etc.), and may also be located at the eNode-B or the AG.
A radio protocol control plane will hereinafter be described with reference to FIG. 2. The radio protocol control plane includes a physical layer, a Medium Access Control (MAC) layer, a Radio Link Control (RLC) layer, and a Radio Resource Control (RRC) layer.
The physical layer acting as the first layer (L1) transmits an Information Transfer Service to an upper layer over a physical channel. The physical layer is connected to the Medium Access Control (MAC) layer (L2 layer) via a transport channel. The MAC layer communicates with the physical layer such that data is communicated between the MAC layer and the physical layer over the transport channel. Data may be communicated among different physical layers. Specifically, data is communicated between a first physical layer of a transmission end and a second physical layer of a reception end.
The MAC layer of the second layer (L2) transmits a variety of services to the RLC (Radio Link Control) layer (L2 layer) over a logical channel. The RLC layer of the second layer (L2) supports transmission of reliable data. A variety of functions of the RLC layer may also be implemented with a function block of the MAC layer. In this case, no RLC layer is necessary.
The RRC (Radio Resource Control) layer located at the uppermost part of the third layer (L3) is defined by the control plane only. The RRC layer controls logical channels, transport channels, and physical channels in relation to configuration, reconfiguration, and release operations of Radio Bearers (RBs). Here, an RB is indicative of a service received from the second layer (L2) to implement data communication between the UE and the E-UTRAN.
A radio protocol user plane will hereinafter be described with reference to FIG. 3. The radio protocol user plane includes the physical layer, the MAC layer, the RLC layer, and a Packet Data Convergence Protocol (PDCP) layer.
The physical layer of the first layer (L1) and the MAC and RLC layers of the second layer (L2) are equal to those of FIG. 2. In order to effectively transmit IP packets (e.g., IPv4 or IPv6) within a radio communication period having a narrow bandwidth, a PDCP layer of the second layer (L2) performs header compression to reduce the size of a relatively large IP packet header containing unnecessary control information.
A detailed description of the RLC layer will hereinafter be described in detail. The principal functions of the RLC layer are for guaranteeing a Quality of Service (QoS) of each RB and transmitting data associated with the QoS. The RB service is indicative of a specific service provided to an upper layer by the second layer of the radio protocol, such that all parts of the second layer affect the QoS. Specifically, it should be noted that the second layer is greatly affected by the RLC layer. The RLC layer assigns an independent RLC entity to each RB to guarantee a unique QoS of the RB. In this case, the RLC entity configures an RLC protocol data unit (PDU) according to the size of radio resources determined by a lower layer (i.e., the MAC layer).
Therefore, when transmitting the RLC PDU to the MAC layer, the RLC entity located at the eNode-B configures data having a predetermined size determined by the MAC entity, and transmits the RLC PDU to the MAC entity. The RLC entity located at the UE also configures the RLC PDU according to the size of radio resources determined by the lower layer (i.e., the MAC layer). Therefore, when transmitting the RLC PDU to the MAC layer, the RLC entity located at the UE configures data having a predetermined size determined by the MAC entity, and transmits the RLC PDU to the MAC entity.